Hmm...I don't think that the US will be the only one to fall, but likely the first.

THE USA:

Has the largest national debt in the world. $8.5 trillion and increases by $1.75 billion a day.

Causes the most pollution in the world per capita.

Is the largest consumer of natural resources (30% of the worlds resources, yet has only 5% of the world's population).

Has the highest MPG consumption per production vehicle of any nation in the world.

I could go on and on, but I'm bored.

Economic or environmental collapse. Within 50 years or so.